This invention relates generally to surgically implantable physiological shunt systems and related flow control devices. More particularly, the present invention relates to shunt systems including one-way flow control devices for controlling the flow of cerebrospinal fluid out of a brain ventricle, and to capacitive elements in such shunt systems designed to reduce overdrainage of cerebrospinal fluid due to the pulsatile nature of cerebrospinal fluid flow.
In the medical arts, to relieve undesirable accumulation of fluids it is frequently necessary to provide a means for draining a fluid from one part of the human body to another in a controlled manner. This is required, for example, in the treatment of hydrocephalus, an ailment usually afflicting infants or children in which fluids accumulate within the skull and exert extreme pressure and skull deforming forces.
In treating hydrocephalus, cerebrospinal fluid accumulated in the brain ventricles is typically drained away utilizing a drainage or shunt system including a catheter inserted into the ventricle through the skull, which is connected to a tube which conducts the fluid away from the brain to be reintroduced into the peritoneal cavity or into the vascular system, as by extending a distal catheter through the patient's jugular vein to the atrium portion of the heart. To control the flow of cerebrospinal fluid and maintain the proper pressure in the brain ventricle, a pump or valve is placed in the conduit between the brain and the peritoneal cavity or the heart. An exemplary flow control device is found in U.S. Pat. No. 4,560,375.
Although such drainage systems have provided successful results, a problem of overdrainage of the cerebrospinal fluid from the brain ventricles sometimes exists. Overdrainage of cerebrospinal fluid may result in excessive reduction of the cerebrospinal fluid pressure within the brain ventricles and predispose the development of a subdural hematoma or hydroma, and excessive reduction of ventricular size leading to shunt obstruction because of impingement of the ventricular walls on the inlet holes of the ventricular catheter. This overdrainage can be caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter. The siphoning effect of hydrostatic pressure may be created by the elevation of the ventricular catheter inlet with respect to the distal catheter outlet (i.e., when the patient sits, stands or is held erect). In order to prevent such overdrainage caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter, siphon control devices have been placed in the conduit, typically between the flow control device and the peritoneal cavity or the heart. An exemplary siphon control device is found in U.S. Pat. No. 4,795,437.
Current cerebrospinal fluid shunts include flow control devices which are unidirectional by design. This characteristic is desirable to prevent reflux of distal fluids into the ventricular system. However, in normal physiology, as demonstrated by continuous magnetic residence imagery (MRI), cerebrospinal fluid flows in a pulsatile nature out of and back into the cerebellar structures as driven by increases and decreases in blood pressure. This pulsatile flow is compromised with the introduction of a one-way valve in the treatment of obstructive hydrocephalus.
Present flow control devices, by their nature, rectify the pulsatile normal flow (analogous to alternating current flow) of the cerebrospinal fluid into an abnormal uni-directional flow (analogous to electrical direct current flow). This can cause an increase in flow rate (overdrainage) due to the continuous expulsion of cerebrospinal fluid out of the ventricular system without allowing the natural return. Proximally induced overdrainage of cerebrospinal fluid often requires revision due to obstructed ventricular catheters.
Accordingly, there has been a need for a surgically implantable shunt system capable of reducing overdrainage of cerebrospinal fluid due to the pulsatile nature of cerebrospinal fluid flow. In this regard, a capacitive element is needed which allows for the placement of a uni-directional valve in the shunt system to prevent reflux while accommodating proximal pulsatile flow within the ventricular system. Additionally, such a novel capacitive element is needed which may be utilized in connection with existing cerebrospinal fluid flow control devices. The present invention fulfills these needs and provides other related advantages.